2D DEM of Ice Rubble: the effect of rate-dependent friction.

The friction coefficient of ice on ice is usually modeled as a constant. However, theory and experimental data show that ice-ice friction depends on the speed of sliding. In this paper we incorporate a rate-dependent friction coefficient into 2D discrete element method simulations of ice ensemble behaviour. Friction is high (0.7) at low sliding speeds (10-2 ms-1) and decreases log-linearly between these values. We show qualitatively and quantitatively how this affects the overall dynamics of a shear box experiment

Properties of thermo-elastic waves in saline ice

The thermal expansion of saline ice is accompanied by the migration of liquid brine through porous space in the ice. Two previous models of this thermal expansion, proposed by Malmgren (1927) and Cox (1983), assume, respectively, zero and infinite permeability of saline ice by liquid brine. In the present paper theoretical investigations, based on Darcy’s law, are used to describe thermo-elastic waves in saline ice, generated as the ice surface warms or cools. Characteristics of these thermo-elastic waves are analyzed for different values of the permeability of sea ice by brine, including zero and infinite values. The model matches known behaviour with these extreme permeabilities, and extends this understanding to sea ice with finite, non-zero permeability

Acoustic emissions from in situ compression and indentation experiments on sea ice

We present results from measurement of acoustic emissions (AE) during compression and indentation of natural sea ice in situ. We show that AE amplitudes are associated with load, so that periods of loading and unloading, and cyclic oscillations in loading during indentation, can be determined from AE records as well as from load measurements. We show that AE measured during these experiments obeys Gutenberg-Richter-type scaling laws, implying that the crack distribution within the sea ice is self-similar. We show that b-values, which indicate the ratio of small cracks to large cracks, decrease during loading, tending towards a value around 1 at failure, and increase again when loading is removed. This suggests that AE can be used to measure, non-invasively, damage and healing of natural sea ice. We conclude by discussion practical applications of these results, and opportunities for further development of AE measurement as a tool for understanding cracking in ice

An investigation of relative thermal expansion of ice and steel

We report the results of a number of experiments conducted by changing the temperature of a steel pipe containing ice. We measure the strain in the ice and the temperature at a frequency of 1Hz using sensors based on fiber Bragg gratings. When the temperature of the apparatus changes, the steel and ice expand or contract at different rates, and so there is the potential for the ice and steel to move relative to each other. The steel pipe constrains the expansion of the ice in two dimensions. Further, cohesion and friction between the ice and steel may limit the movement of the ice in the third dimension. The measured strain therefore allows us to make inferences about the interaction between the ice and the pipe. We find a coefficient of thermal expansion in free ice comparable to literature values (around 51x10-6K-1) but that the effective expansion coefficient varies depending on how the ice is constrained. We also report on the results of similar experiments with saline ice

The influence of marternal handicap on growth and reproduction in sheep

Ooie met enkel lammers het of voldoende vore ontvang om liggaamskondisie gedurende laktasie te handhaff (hoe peil) of die hoeveel-heid voer is verminder sodat n gemiddelde verlies van naastenby 20% in liggausmaan teweeggebring (lae peil). Die lammers het vrye toe-gang tot ru-en konsentraatvoere gehad. Na speen is die lammers gevoer om vinnige groei te bevorder. Die sogende lammers van ooie op die lae voedingspeil het nie merkbaar groter hoevoelhede ruvoer en konsentraat ingeneem as soortgelyke lammers van ooie op die hoe peil nie. Ondervoeding van die lakterende ooie het die ooi lammers by speen beduidend verlaag (P=0,001). Gedurende die naspeen tydperk is  hierdie agterstand in groei van die lammers geleidelik verminder, maar was nog merkbaar by geboorte van hul eerste lam.SUMMARYEwes with single lambs received either sufficient feed to maintain body condition during (high plane) or the qunatity of feed was reduced so as to result in an average loss of approximately 20% in bodymass (low plane). The suckling lambs had free access to roughage and concentrate feeds. After weaning the lambs were fed so as to promote rapid growth. The lambs suckled ny ewes on the low plane did not consume appreciably greater quantities of roughage and concentrate than similar lambs reared by ewes which were adequately fed. Under-feeding of the lactating ewes significantly reduced the bodymass of their ewe-lambs at weaning (P=0,001). The deficit in growth of the lambs was gradually reduced during the post-weaning period, but was still evident in their first parturition.

Ice properties in ISO 19906's second edition

The second edition of ISO 19906 Arctic Offshore structures was issued in 2019. In this paper, we describe the changes that were made to sections dealing with ice properties and discuss the relationship between them and ice actions. The changes can be divided into five groups: 1) Physical properties (temperature, density and porosity), 2) modulus of elasticity, 3) ice friction, 4) mechanical properties in level ice (uniaxial and multi-axial compressive strength, flexural strength and borehole jack strength), and 5) the keel properties of first-year ridge (Mohr-Coulomb, macro-porosity). The standard is written in such a way so that simple approaches in design guidelines complement more elaborate models. Both currently face at least three challenges, namely, the lack of full-scale data, a complicated physical environment, and a lack of understanding of the deformation mechanisms taking place in the ice

The effect of ice rubble on ice-ice sliding

Ice deformation processes in the Arctic can generate ice rubble. Many situations arise where ice fragments of varying size separate sea ice floes. While the shear forces between sea ice floes in direct contact with each other are controlled by ice-ice friction, what is not known is how the slip of the floes is affected by the presence of rubble between the sliding surfaces. We present the result of field experiments undertaken on sea ice in the Barents Sea. A doubledirect-shear experiment was done on floating sea ice in the field, with the addition of rubble ice between the sliding surfaces. This was achieved by pulling a floating ice block through a cut channel of open water 3m long, where broken ice filled the gap between the block and the channel sides. The displacement of the block and the force needed to move the block were measured. The time that the block was held motionless to allow the rubble to consolidate was recorded - this ranged from seconds to several hours. We found that the 'hold time' controls the maximum force needed to move the block. The relation between hold time and force is highly non-linear from which we deduce thermal consolidation is the controlling mechanism

The influence of ice structure on thermo-elastic waves in saline ice

We formulate a structural model of saline ice and describe a model solution describing the propagation of thermo-elastic waves. Thermo-elastic waves are excited by periodical oscillations of the ice surface temperature. The properties of these thermo-elastic waves are determined by the mean ice temperature (background temperature), the ice salinity and the amount of liquid brine trapped in closed brine pockets. Results from an experiment, measuring thermo-elastic waves in ice, performed in the UNIS cold laboratory, are described. The characteristics of these thermo-elastic waves are compared with the theory. It is shown that amount of liquid brine trapped in closed brine pockets is an important variable in describing how the ice deforms under oscillating background temperature

Elasticity and viscosity of ice measured in the experiment on wave propagation below the ice in HSVA ice tank

An experiment on the propagation of flexural-gravity waves was performed in the HSVA ice tank in 2018. Physical characteristics of the water-ice system were measured in different locations in the tank during the tests, with several sensors deployed in the water, on the ice and in the air. Periodical waves with frequencies of 0.5-1.5 Hz were generated by HSVA wave maker during 10 min in each test. The phase speeds and wave damping associated with anelastic deformations of ice were analyzed in the paper. Elastic modulus of ice was calculated for each wave period from the dispersion equation of flexural gravity waves where measured values of wave frequencies and wave speeds were substituted. Viscous coefficient of ice was calculated after the analysis of wave damping. Obtained values have relatively big dispersion which can be explained by natural variability of ice properties

Laboratory Investigations of the Bending Rheology of Floating Saline Ice and Physical Mechanisms of Wave Damping In the HSVA Hamburg Ship Model Basin Ice Tank

An experimental investigation of flexural-gravity waves was performed in the Hamburg Ship Model Basin HSVA ice tank. Physical characteristics of the water-ice system were measured in several locations of the tank with a few sensors deployed in the water and on the ice during the tests. The three-dimensional motion of ice was measured with the optical system Qualisys; water pressure was measured by several pressure sensors mounted on the tank wall, in-plane deformations of the ice and the temperatures of the ice and water were measured by fiber optic sensors; and acoustic emissions were recorded with compressional crystal sensors. The experimental setup and selected results of the tests are discussed in this paper. Viscous-elastic model (Burgers material) is adopted to describe the dispersion and attenuation of waves propagating below the ice. The elastic modulus and the coefficient of viscosity are calculated using the experimental data. The results of the measurements demonstrated the dependence of wave characteristics from the variability of ice properties during the experiment caused by the brine drainage. We showed that the cyclic motion of the ice along the tank, imitating ice drift, and the generation of under ice turbulence cause an increase of wave damping. Recorded acoustic emissions demonstrated cyclic microcracking occurring with wave frequencies and accompanying bending deformations of the ice. This explains the viscous and anelastic rheology of the model ice